1. Field of The Invention
The present invention generally relates to the field of design and construction of archery bows. More particularly, the present invention relates to the field of an improvement on the limb bolt assembly used on recurve bows.
2. Description of The Prior Art
Most of today's recurve bows are three-piece takedown units. A typical three-piece recurve bow has a center riser section, an upper limb and a lower limb. The upper and lower limbs are respectively mounted to the upper and lower ends of the center riser by limb bolts. The limb bolts essentially serve two main functions. First, they are used for mounting the upper and lower limbs to the center riser. Second, they are used for adjusting the poundage of the bow. Some recurve bows further utilize the same limb bolt for adjusting the tiller of the bow. As used conventionally, "poundage" refers to the overall strength of the limbs measured in pounds when the bow is drawn to a standard distance, e.g., twenty-eight inches (28"), and "tiller" refers to the balance of the relative strengthening or weakening of the upper and lower limbs of the bow.
On prior art recurve bows, the limb bolts are usually simple screw bolts with a hexagonal head or Allen wrench socket. An archer can use a wrench or Allen wrench to thread the limb bolt to fasten the upper or lower limb, or adjust the poundage and/or tiller of the bow. However, this arrangement has several disadvantages. First, since the limb bolts are directly engaged with the upper or lower limb of the recurve bow, the repeated vibration of the limbs during the releasing of the arrow often causes the limb bolts to become loose and the poundage settings thrown off. Second, when threading the limb bolt to adjust the poundage and/or tiller of the bow, an archer has no way of knowing when the poundage or tiller is properly adjusted. Therefore, the archer has to repeat the adjustment by time consuming experiments every time to obtain a proper adjustment.
For example, a sixty-pound recurve bow will typically build up sixty pounds (60 lb.) at about a twenty-eight-inch (28") draw. Therefore, to tune in a sixty-pound recurve bow, an archer needs to adjust the limb bolts of the bow and measure the poundage of the bow on a scale machine at twenty-eight-inch draw, until the poundage is set correctly at sixty pounds. However, when the limb bolts become loose because of the vibration of the limb during shooting and need to be readjusted to restore the correct poundage or balanced tiller, the archer has no way to know the previous rotational position of the limb bolts, and has to repeat the whole tuning procedure again by using the scale machine and/or other measuring devices. This process often becomes very time consuming, and very inconvenient and impractical during archery championships, outdoor sporting events or hunting trips.
The following six (6) prior art patents were found to be pertinent to mounting screws with indication means.
1. U.S. Pat. No. 2,830,486 issued to Dillon on Apr. 15, 1958 for "Resilient Nut With Tension Indicating Means" (hereafter "the Dillon Patent"). PA1 2. U.S. Pat. No. 3,060,731 issued to Adise on Oct. 30, 1962 for "Motion Translator" (hereafter "the Adise Patent"). PA1 3. U.S. Pat. No. 3,602,186 issued to Popenoe on Aug. 31, 1971 for "Opti-Mechanical Stress-Strain Indicator" (hereafter "the Popenoe Patent"). PA1 4. U.S. Pat. No. 3,823,639 issued to Liber on Jul. 16, 1974 for "Tension Indicating Fastener" (hereafter "the Liber Patent"). PA1 5. U.S. Pat. No. 3,886,840 issued to Bossler on Jun. 3, 1975 for "Bolt Head Which Measures And Maintains Preload" (hereafter "the Bossler Patent"). PA1 6. U.S. Pat. No. 5,165,831 issued to Yager et al. on Nov. 24, 1992 for "Capscrew Head Markings For Torque-Angle Tightening" (hereafter "the Yager Patent").
The Dillon Patent discloses a resilient nut with a tension indicating means. It includes a rectangular block having a vertical bore extending therethrough from top to bottom. An indicator is provided with one or more calibration lines positioned at any suitable point along the edge of the block for measuring the flexure.
The Adise Patent discloses a motion translator. An indicator card is carried by an arm at its free end. The card is provided with a uniformly graduated scale.
The Popenoe Patent discloses an opti-mechanical stress-strain indicator. It includes a bolt which has a large bore, and a pin disposed within the bore. The stress is measured by the color change of the fluid within the large bore.
The Liber Patent discloses a tension indicating fastener. It is utilized to support mine shaft roofs. The tension of the mine bolts is measured by a photoelastic member in the form of photoelastic fringes for reading by reflection polariscope.
The Bossler Patent discloses a bolt head which measures and maintains a preload. An indicator-washer is mounted at the periphery of the upper recess, closing the recess and being relatively non-deflecting with respect to the ring, so that the relative position of the indicator pin and indicator-washer or ring is a function of the preload.
The Yager Patent discloses a capscrew head marking for torque-angle tightening. It includes a fastener which has an externally threaded shank portion, a torque receiving portion integrally connected to one end of the shank portion and an outwardly extending flange located between the shank portion and the torque receiving portion.
It can be seen that none of the prior art mounting screws can be suitably used as the limb bolts on a recurve bow where the connections between the upper and lower limbs and the center riser are subject to severe vibrations during the releasing of the arrow. Therefore, it is desirable to develop a new limb bolt assembly for recurve bows. It is desirable that the new limb bolt assembly can tightly mount the upper or lower limb to the center riser of the recurve bow such that the vibration from the releasing of the arrow will not cause the new limb bolt assembly to become loose. It is further desirable that the new limb bolt assembly provide a quick reference of the correct poundage and tiller adjustment to an archer.